1. Field of the Invention
The invention relates to a power pulling arrangement and has particular utility in the electrical field as an aid to pulling cable and wire or cable and wire combination through installed conduit.
2. Brief Description of the Prior Art
Persons skilled in the construction field will be familiar with the fact that sound safety practice requires that all current carrying cable and wire be installed in appropriately sized conduit which, for example, may be arranged to interconnect service entrance box and distribution box centers. Usually employed construction procedure requires that the service entrance and distribution box centers, the interconnecting conduit and like be placed in the new building at an early stage in the construction thereof. At this point in such construction the boxes and conduit are empty and the electrical conductors are installed at a later stage of the construction. In large commercial and industrial building, the conduit employed may be required to have a diameter of two to six inches or even greater and when installed will be bent at various angles, offset, elbowed or the like.
The conductors employed in conduit of the sizes here under consideration frequently have nominal diameters of an inch or more. Material economy dictates that as many conductors as possible be placed in each conduit. The length of conduit run is, of course, variable depending upon the physical features of the building, however, runs of several hundred feet are not uncommon. These facts, namely, the length and erratic path of the conduit run, the size and number of conductors placed in each conduit make the job of pulling the conductors through said conduit an extremely difficult one.
To better understand the herein disclosed invention brief consideration should be given to the procedure followed in conductor installation. Initially, a very light lead line is fed through the conduit run. This may be accomplished by first shooting a small weight with the line attached thereto through the conduit. The lead line is then connected to a steel cable or pull rope (manila or plastic) which is fed through the run. A mechanical connection is then provided between the cable or rope and the conductors. The cable or rope and the connected conductors are then pulled through the conduit. Where metal conduit is employed a steel pull cable may be used. Recently however aluminum pipe has been employed in large diameter conduit. It has the advantage of light weight and ductility which facilitates bending and installation. With aluminum conduit a rope pull line is more desirable in that a steel line tends to gouge the relatively soft aluminum conduit surface.
To develop the pulling force required, prior art practice has dictated that a wide variety of force multiplying devices be used. For example, block and tackle, windlass and powered winches have been used. Because of the wide difference of the physical features of each installation, the equipment referred to above was usually specially rigged for each job. Set up time alone, therefore, represented an important cost factor for each job. Frequently, set up time could not even be estimated accurately before the job was actually begun. In many cases special temporary scaffolding would have to be built before conductor pulling could commence.
Problems and difficulties have been encountered when employing such force multiplying devices which stem largely from the fact that the pulling force may exceed the tensile strength of the pull line which will sever or break the pull line. Such an occurrence may result in injury to nearby workmen or damage to property.
Therefore, a long standing need has existed to provide a cable or wire puller which provides increased pulling power with an extra measure of safety.